1. Field of the Invention
This invention relates to a cartridge case for a telescoped ammunition round and, more particularly, to a cartridge case providing improved handling characteristics for spent rounds.
2. Discussion of the Related Art
Telescoped ammunition is well known in the ordnance art. Typically, a telescoped ammunition round includes a propellant charge having an axial bore or cavity, a projectile housed within, usually entirely within, the axial bore of the propellant charge and a tubular case around the outside of the propellant charge forming the exterior surface of the round. When a telescope round of ammunition is loaded into the firing chamber of a gun, the projectile, being housed within the propellant charge, is not seated in the barrel of the gun as would be the projectile of a round of conventional ammunition.
When the telescoped round is fired, the projectile is forced forward into the barrel of the gun and becomes seated in the barrel. The firing force is also applied as an outward force to the case and, accordingly, tends to cause radially outward deformation or deflection of the case. It is generally understood that during firing these forces cause not only an increase in the diameter of the case, but also a corresponding increase in diameter of the firing chamber. After firing, the firing chamber returns to its original dimensions. The tubular case of the telescoped ammunition round, e.g., a tubular steel case, may be permanently deformed during firing by radial expansion beyond its limits of elastic deformation. In this case, the spent ammunition round may lock in the firing chamber due to resulting interference between the case and the chamber wall. Such interference inhibits rapid, automatic loading and firing.
Telescoped ammunition differs from conventional ammunition in that a conventional cartridge has a tapered case that allows it to be extracted easily from the firing chamber after firing. While the cartridge case of a conventional round typically undergoes some permanent deformation, specifically, radial expansion, as a result of the Pressures developed during firing, the tapered design allows the spent case to be removed from the firing chamber with minimal resistance once the initial breakaway force is overcome. The tapered case of conventional rounds requires, however, that cartridge insertion and subsequent case extraction be accomplished sequentially from the same end of the firing chamber. In contrast, a telescoped cartridge is basically a straight cylinder so that insertion and extraction can occur simultaneously in the same direction at opposite ends of an open-ended firing chamber. Advantageously, this allows the incoming round to be used as the mechanism for pushing the fired case out of the chamber, thereby resulting in considerable simplification of the gun mechanism. Because of the cylindrical shape of the cartridge case, however, the spent case would resist extraction from the chamber even beyond an initial breakaway force if the case had suffered permanent deformation, i.e., radial expansion, during firing.
To prevent permanent deformation of the cartridge case of a telescoped ammunition round, a pressure relief feature or mechanism of some sort is required, whereby firing pressures building up within the case can escape other than merely out the forward end of the case behind the advancing projectile.
It is known to use a plastic case in an automatic fixture for telescoped ammunition. Plastic is not capable, however, without substantial risk of failure, of handling the ballistic cycle loads in a typical firing environment temperature range of -65.degree.F. to +165.degree.F.
It is also known to fabricate the case of a telescoped ammunition round from two sections which then are bonded together. For example, U.S. Pat. No. 3,892,181 to Goldin teaches a flat telescoped cartridge case which is formed of two separate, identical pieces joined by ultrasonic welding. This case, however, presents the same disadvantages mentioned above regarding a solid tubular steel case in that it may be permanently deformed during firing.
In U.S. Pat. No. 4,604,954 to Clarke et al a telescoped ammunition round is disclosed having a pressure relief feature to avoid permanent radial deformation of the casing. Specifically, the tubular casing surrounding the propellant charge has two longitudinal splits dividing the casing into two substantially identical halves. The casing halves can separate during firing and, thus, while sustaining firing pressure created by the propellant charge, avoid permanent deformation. An end cap assembly couples adjacent ends of the halves of the tubular casing to each other. Such dual split cartridge case ammunition rounds, however, while functional, present certain difficulties in establishing a durable hermetic seal. Ammunition rounds must be durable and able to withstand prolonged exposure to a wide variety of environmental conditions and also physical impacts during handling, transportation, etc. It is highly desirable, therefore, to provide a telescoped ammunition cartridge case which provides the necessary pressure relief feature, yet which does not have the disadvantages of the split case described above.
The object of the present invention is to provide a cartridge case for a telescoped ammunition round which satisfies the need for a pressure release feature to avoid casing lock-up in the firing chamber. These and other objects and advantages of the present invention will be understood from the following disclosure and discussion thereof.